Carbohydrates are considered as the most abandunt organic matter. The things we meet up as sugars and flour in day-to-day life belong to the group of Carbohydrates. All Carbohydrates have the general formula: Cx(H2O)y. Carbohydrates can be divided into 3 classes;
- Monosaccharids
- Disaccharides
- Polysaccharides
MONOSACCHARIDES
Monosaccharides are the building blocks of other Carbohydrates. Their molecular structures are simple. They show the following characteristics in common;
- Sweet in taste
- Soluable in water
- Can be crystellined(Can be made into crystals)
- General formula is (CH2O)n
- Show reducing properties (Monosaccharides are reducing sugars)
| Reducing Sugars? |
All the monosaccharides are reducing sugars. They can reduce Benedict's Solution. Benedict's Solution contains Cu2+ ions, which are blue in colour. Monosaccharides reduce Cu2+ ions to Cu+ ions, which gives "brick-red clour" to the solution.
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Monosaccharides are classified according to the number of Carbon(C) atoms in the molecule.
3 Carbon atoms -> Triose [Eg: Glyceraldehyde]
4 Carbon atoms -> Tetrose [Eg: Erythrose]
5 Carbon atoms -> Pentose [Eg: Ribose]
6 Carbon atoms -> Hexose [Eg: Glocose]
Of these, Pentoses and Hexoses are the most common.
Aldoses and Ketoses
In all monosaccharides, all the Carbon(C) atoms, except one, have hydroxyl groups(-OH) attached to them. The Carbon(C) atom which has no hydroxyl group(-OH) is either a part of an Aldehyde group, or a part of a Keto group. In case of an aldehyde group, the sugar is called an Aldose or an Aldo Sugar. In case of a keto group, the sugar is a Ketose or a Keto Sugar.
Ring Structures
Pentoses and Hexoses are longer molecules. Due to the bond angles of Carbon(C) atoms, the sugar molecule bends: forming a stable ring structure.
| Formation of the Ring Structure of Glucose |
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| The first Carbon atom(C1) combines with the Oxygen atom of the fifth Carbon atom(C5) |
In Pentoses, the first Carbon atom(C1) combines with the Oxygen atom of the fourth Carbon atom(C4)
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